Perl Reference Guide for Perl version 5.000

Perl program designed and created by Larry Wall

Reference guide designed and created by Johan Vromans

Contents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.

Command line options Literals Variables Operators Statements Subroutines, packages and modules Object oriented programming Arithmetic functions Conversion functions Structure conversion String functions Array and list functions Regular expressions Search and replace functions File test operators File operations Input / Output Formats Directory reading routines System interaction Networking SystemV IPC Miscellaneous Info from system files Special variables Special arrays Environment variables The perl debugger

Rev. 5.000.0

Perl Reference Guide

Conventions fixed THIS THIS word RET

[


]

denotes literal text. means variable text, i.e. things you must fill in. means that THIS will default to $_ if omitted. is a keyword, i.e. a word with a special meaning. denotes pressing a keyboard key. denotes an optional part.

1. Command line options -a -c -d

turns on autosplit mode when used with -n or -p. Splits to @F. checks syntax but does not execute. runs the script under the debugger. Use “-de 0” to start the debugger without a script.

-D NUMBER sets debugging flags. -e COMMANDLINE may be used to enter one line of script. Multiple -e commands may be given to build up a multi-line script. -F REGEXP specifies a regular expression to split on if -a is in effect. -i EXT files processed by the < > construct are to be edited in-place. -I DIR with -P: tells the C preprocessor where to look for include files. The directory is prepended to @INC. -l [ OCTNUM ] enables automatic line ending processing, e.g. -l013. -n assumes an input loop around your script. Lines are not printed. -p assumes an input loop around your script. Lines are printed. -P runs the C preprocessor on the script before compilation by perl. -s interprets “-xxx” on the command line as switches and sets the corresponding variables $xxx in the script. -S uses the PATH environment variable to search for the script. -T forces taint checking. -u dumps core after compiling the script. To be used with the undump program (where available). -U allows perl to do unsafe operations. -v prints the version and patchlevel of your perl executable. -w prints warnings about possible spelling errors and other error-prone constructs in the script. -x [ DIR ] extracts perl program from input stream. If DIR is specified, switches to this directory before running the program. -0 VAL (that’s the number zero) designates an initial value for the record separator $/. See also -l.

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2. Literals Numeric: 123 1_234 123.4 5E-10 0xff (hex) 0377 (octal). String: ’abc’ literal string, no variable interpolation nor escape characters, except \’ and \\. Also: q/abc/. Almost any pair of delimiters can be used instead of /


/. "abc" Variables are interpolated and escape sequences are processed. Also: qq/abc/. Escape sequences: \t (Tab), \n (Newline), \r (Return), \f (Formfeed), \b (Backspace), \a (Alarm), \e (Escape), \033(octal), \x1b(hex), \c[ (control). \l and \u lowcase/upcase the following character; \L and \U lowcase/upcase until a \E is encountered. \Q quote regexp characters until a \E is encountered. ‘COMMAND‘ evaluates to the output of the COMMAND. Also: qx/COMMAND/. Array: (1,2,3). () is an empty array. (1..4) is the same as (1,2,3,4). Likewise (’abc’..’ade’). qw/foo bar


/ is the same as (’foo’,’bar’,


). Array reference: [1,2,3]. Hash (associative array): (KEY1, VAL1, KEY2, VAL2,


). Also: (KEY1 => VAL1, KEY2 => VAL2,


). Hash reference: {KEY1, VAL1, KEY2, VAL2,


}. Code reference: sub { STATEMENTS } Filehandles: STDIN, STDOUT, STDERR, ARGV, DATA. User-specified: HANDLE, $VAR. Globs: evaluates to all filenames according to the pattern. Use “” or “glob $VAR” to glob from a variable. Here-Is: {’Feb’}. last index of array @var. the entire array; in scalar context: the number of elements in the array. a slice of array @var.

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Perl Reference Guide @var{’a’,’b’} a slice of %var; same as ($var{’a’},$var{’b’}). %var the entire hash; in scalar context: true if the hash has elements. $var{’a’,1,...} emulates a multi-dimensional array. (’a’..’z’)[4,7,9] a slice of an array literal. PKG::VAR a variable from a package, e.g. $pkg::var, @pkg::ary. \OBJECT reference to an object, e.g. \$var, \%hash. *NAME refers to all objects represented by NAME. “*n1 = *n2” makes n1 an alias for n2. “*n1 = \$n2” makes $n1 an alias for $n2. You can always use a { BLOCK } returning the right type of reference instead of the variable identifier, e.g. ${


}, &{


}. $$p is just a shorthand for ${$p}.

4. Operators Exponentiation. * / Addition, subtraction, multiplication, division. Modulo division. ˆ Bitwise and, bitwise or, bitwise exclusive or. Dereference operator. \ Reference (unary). ! ˜ Negation (unary), bitwise complement (unary). ++ -- Auto-increment (magical on strings), auto-decrement. = = != Numeric equality, inequality. eq ne String equality, inequality. < > Numeric less than, greater than. lt gt String less than, greater than. = Numeric less (greater) than or equal to. le ge String less (greater) than or equal. cmp Numeric (string) compare. Returns -1, 0 or 1. =˜ !˜ Search pattern, substitution, or translation (negated). .. Bistable (scalar context) or enumeration (array context). ? : Alternation (if-then-else) operator. , Comma operator, also list element separator. You can also use =>. not low-precedence negation. and low-precedence and. or xor low-precedence or, xor. A “list” is a list of expressions, variables or lists. An array variable or an array slice may always be used instead of a list. All perl functions can be used as list operators, in which case they have very high or very low precedence, depending on whether you look at the left side of the operator or at the right side of it. Only the operators not, and, or and xor, have lower precedence. You can always put parentheses around the parameter lists to avoid problems.

** + % & | >> || .

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5. Statements Every statement is an expression, optionally followed by a modifier, and terminated with a semicolon. The semicolon may be omitted if the statement is the final one in a BLOCK. Execution of expressions can depend on other expressions using one of the modifiers if, unless, while or until, e.g.: EXPR1 if EXPR2 ; EXPR1 until EXPR2 ; Also, by using one of the logical operators ||, && or ?:, e.g.: EXPR1 || EXPR2 ; EXPR1 ? EXPR2 : EXPR3 ; Statements can be combined to form a BLOCK when enclosed in {}. BLOCKs may be used to control flow: if (EXPR) BLOCK [ [ elsif (EXPR) BLOCK ... ] else BLOCK ] unless (EXPR) BLOCK [ else BLOCK ] [ LABEL: ] while (EXPR) BLOCK [ continue BLOCK ] [ LABEL: ] until (EXPR) BLOCK [ continue BLOCK ] [ LABEL: ] for ( [ EXPR ] ; [ EXPR ] ; [ EXPR ] ) BLOCK [ LABEL: ] foreach VAR (ARRAY) BLOCK [ LABEL: ] BLOCK [ continue BLOCK ] Program flow can be controlled with: goto LABEL

Continue execution at the specified label. last [ LABEL ] Immediately exits the loop in question. Skips continue block. next [ LABEL ] Starts the next iteration of the loop. redo [ LABEL ] Restarts the loop block without evaluating the conditional again. Special forms are: do BLOCK while EXPR ; do BLOCK until EXPR ; which are guaranteed to perform BLOCK once before testing EXPR, and do BLOCK

which effectively turns BLOCK into an expression.

6. Subroutines, packages and modules &SUBROUTINE LIST Executes a SUBROUTINE declared by a sub declaration, and returns the value of the last expression evaluated in SUBROUTINE . SUBROUTINE can be an expression yielding a reference to a code object. The & may be omitted if the subroutine has been declared before being used. bless REF [ , PACKAGE ] Turns the object REF into an object in PACKAGE. Returns the reference. caller [ EXPR ] Returns an array ($package,$file,$line,...) for a specific subroutine call.

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Perl Reference Guide “caller” returns this info for the current subroutine, “caller(1)” for the caller of this subroutine etc.. Returns false if no caller. do SUBROUTINE LIST

Deprecated form of &SUBROUTINE . goto &SUBROUTINE Substitutes a call to SUBROUTINE for the current subroutine. import MODULE [ LIST ] Imports the named subroutines from MODULE. no MODULE [ LIST ] Cancels imported semantics. See use. package NAME

Designates the remainder of the current block as a package. require EXPR If EXPR is numeric, requires Perl to be at least that version. Otherwise EXPR must be the name of a file that is included from the perl library. Does

not include more than once, and yields a fatal error if the file does not evaluate to a true value. If EXPR is a bare word, assumes extension “.pm” for the name of the file. return EXPR

Returns from a subroutine with the value specified. sub NAME { EXPR ;


} Designates NAME as a subroutine. Parameters are passed by reference as array @_. Returns the value of the last expression evaluated. [ sub ] BEGIN { EXPR ;


} Defines a setup BLOCK to be called before execution. [ sub ] END { EXPR ;


} Defines a cleanup BLOCK to be called upon termination. tie VAR, PACKAGE, [ LIST ] Ties a variable to a package that will handle it. Can be used to bind a dbm or ndbm file to a hash. untie VAR

Breaks the binding between the variable and the package. use MODULE [ LIST ] Import semantics from the named module into the current package.

7. Object oriented programming Perl rules of object oriented programming:  An object is simply a reference that happens to know which class it belongs to. Objects are blessed, references are not.  A class is simply a package that happens to provide methods to deal with object references. If a package fails to provide a method, the base classes as listed in @ISA are searched.  A method is simply a subroutine that expects an object reference (or a package name, for static methods) as the first argument. Methods can be applied with: method OBJREF PARAMETERS or OBJREF->method PARAMETERS

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8. Arithmetic functions abs EXPR

Returns the absolute value of its operand. atan2 Y, X

Returns the arctangent of Y/X in the range - to  . cos EXPR

Returns the cosine of EXPR (expressed in radians). exp EXPR

Returns e to the power of EXPR. int EXPR

Returns the integer portion of EXPR. log EXPR

Returns natural logarithm (base e) of EXPR. rand [ EXPR ] Returns a random fractional number between 0 and the value of EXPR. If EXPR is omitted, returns a value between 0 and 1. sin EXPR

Returns the sine of EXPR (expressed in radians). sqrt EXPR

Return the square root of EXPR. srand [ EXPR ] Sets the random number seed for the rand operator. time Returns the number of seconds since January 1, 1970. Suitable for feeding to gmtime and localtime.

9. Conversion functions chr EXPR

Returns the character represented by the decimal value EXPR. gmtime EXPR

Converts a time as returned by the time function to a 9-element array (0:$sec, 1:$min, 2:$hour, 3:$mday, 4:$mon, 5:$year, 6:$wday, 7:$yday, 8:$isdst) with the time analyzed for the Greenwich timezone. $mon has the range 0..11 and $wday has the range 0..6. hex EXPR

Returns the decimal value of EXPR interpreted as an hex string. localtime EXPR

Converts a time as returned by the time function to ctime(3) string. In array context, returns a 9-element array with the time analyzed for the local timezone. oct EXPR

Returns the decimal value of EXPR interpreted as an octal string. If EXPR starts off with 0x, interprets it as a hex string instead. ord EXPR

Returns the ascii value of the first character of EXPR. vec EXPR, OFFSET, BITS Treats string EXPR as a vector of unsigned ints, and yields the bit at OFFSET. BITS must be between 1 and 32. May be used as an lvalue.

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10. Structure conversion pack TEMPLATE, LIST

Packs the values into a binary structure using TEMPLATE. unpack TEMPLATE, EXPR

Unpacks the structure EXPR into an array, using TEMPLATE. TEMPLATE is a sequence of characters as follows: a / A Ascii string, null / space padded b / B Bit string in ascending / descending order c / C Native / unsigned char value f / d Single / double float in native format h / H Hex string, low / high nybble first. i / I Signed / unsigned integer value l / L Signed / unsigned long value n / N Short / long in network (big endian) byte order s / S Signed / unsigned short value u / p Uuencoded string / Pointer to a string v / V Short / long in VAX (little endian) byte order x / @ Null byte / null fill until position X Backup a byte Each character may be followed by a decimal number which will be used as a repeat count, an * specifies all remaining arguments. If the format is preceded with %N, unpack returns an N-bit checksum instead. Spaces may be included in the template for readability purposes.

11. String functions chomp LIST

Remove line endings from all elements of the list; returns the (total) number of characters removed. chop LIST

Chops off the last character on all elements of the list; returns the last chopped character. crypt PLAINTEXT, SALT

Encrypts a string. eval EXPR EXPR is parsed and executed as if it were a perl program. The value

returned is the value of the last expression evaluated. If there is a syntax error or runtime error, an undefined string is returned by eval, and $@ is set to the error message. See also eval in section “Miscellaneous”. index STR, SUBSTR [ , OFFSET ] Returns the position of SUBSTR in STR at or after OFFSET. If the substring is not found, returns -1 (but see $[ in section “Special variables”). length EXPR

Returns the length in characters of the value of EXPR. lc EXPR

Returns a lowercased version of EXPR. lcfirst EXPR

Returns EXPR with the first character lowercased.

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Perl Reference Guide quotemeta EXPR Returns EXPR with all regexp meta-characters quoted. rindex STR, SUBSTR [ , OFFSET ]

Returns the position of the last SUBSTR in STR at or before OFFSET. substr EXPR, OFFSET [ , LEN ] Extracts a substring out of EXPR and returns it. If OFFSET is negative, counts from the end of the string. May be used as an lvalue. uc EXPR

Returns an upcased version of EXPR. ucfirst EXPR

Returns EXPR with the first character upcased.

12. Array and list functions delete $HASH{KEY}

Deletes the specified value from the specified hash. Returns the deleted value unless HASH is tied to a package that does not support it. each %HASH Returns a 2-element array consisting of the key and value for the next value of the hash. Entries are returned in an apparently random order. When the hash is entirely read, a null array is returned. The next call to each after that will start iterating again. exists EXPR

Checks if the specified hash key exists in its hash array. grep EXPR, LIST grep BLOCK LIST Evaluates EXPR or BLOCK for each element of the LIST, locally setting $_

to refer to the element. Modifying $_ will modify the corresponding element from LIST. Returns the array of elements from LIST for which EXPR returned true. join EXPR, LIST

Joins the separate strings of LIST into a single string with fields separated by the value of EXPR, and returns the string. keys %HASH Returns an array with of all the keys of the named hash. map EXPR, LIST map BLOCK LIST Evaluates EXPR or BLOCK for each element of the LIST, locally setting $_

to refer to the element. Modifying $_ will modify the corresponding element from LIST. Returns the list of results. pop @ARRAY

Pops off and returns the last value of the array. push @ARRAY, LIST Pushes the values of LIST onto the end of ARRAY. reverse LIST

In array context: returns the LIST in reverse order. In scalar context: returns the first element of LIST with bytes reversed. scalar @ARRAY Returns the number of elements in the array.

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Perl Reference Guide scalar %HASH

Returns a true value if the hash has elements defined. shift [ @ARRAY ] Shifts the first value of the array off and returns it, shortening the array by 1 and moving everything down. If @ARRAY is omitted, shifts @ARGV in main and @_ in subroutines. sort [ SUBROUTINE ] LIST Sorts the LIST and returns the sorted array value. If SUBROUTINE is specified, gives the name of a subroutine that returns less than zero, zero, or greater than zero, depending on how the elements of the array, available to the routine as $a and $b, are to be ordered. SUBROUTINE may be the name of a user-defined routine, or a BLOCK. splice @ARRAY, OFFSET [ , LENGTH [ , LIST ] ] Removes the elements of @ARRAY designated by OFFSET and LENGTH, and replaces them with LIST (if specified). Returns the elements removed. split [ PATTERN [ , EXPR [ , LIMIT ] ] ] Splits a string into an array of strings, and returns it. If LIMIT is specified, splits in no more than that many fields. If PATTERN is also omitted, splits on whitespace. If not in array context: returns number of fields and splits to @_. See also: “Search and replace functions”. unshift @ARRAY, LIST Prepends list to the front of the array, and returns the number of elements in the new array. values %HASH Returns a normal array consisting of all the values of the named hash.

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13. Regular expressions Each character matches itself, unless it is one of the special characters +?.*ˆ$()[]{}|\. These characters can be escaped from their special meaning using a \. . matches an arbitrary character, but not a newline unless it is a single-line match (see m//s). (


) groups a series of pattern elements to a single element. ˆ matches the beginning of the target. In multi-line mode (see m//m) matches also after every newline character. $ matches the end of the line. In multi-line mode matches also before every newline character. [


] denotes a class of characters to match. [ˆ


] negates the class. (


|


|


) matches one of the alternatives. (?# TEXT ) Comment. (?: REGEXP ) Like (REGEXP) but does not make backreferences. (?= REGEXP ) Zero width positive look-ahead assertion. (?! REGEXP ) Zero width negative look-ahead assertion. (? MODIFIER ) Embedded pattern-match modifier. MODIFIER can be one or more of i, m, s or x. Quantified subpatterns match as many times as possible. When followed with a ? they match the minimum number of times. These are the quantifiers: + matches the preceding pattern element one or more times. ? matches zero or one times. * matches zero or more times. {N,M} denotes the minimum N and maximum M match count. {N} means exactly N times; {N,} means at least N times. A \ escapes the immediately following non-alphanumeric character from any special meaning, but it turns most alphanumeric characters into something special: \w matches alphanumeric, including “_”, \W matches non-alphanumeric. \s matches whitespace, \S matches non-whitespace. \d matches numeric, \D matches non-numeric. \A matches the beginning of the string, \Z matches the end. \b matches word boundaries, \B matches non-boundaries. \G matches where the previous m//g search left off. \n, \r, \f, \t etc. have their usual meaning. \w, \s and \d may be used within character classes, \b denotes backspace in this context. Backreferences: \1


\9 refer to matched sub-expressions, grouped with (), inside the match. \10 and up can also be used if the pattern matches that many sub-expressions. See also $1


$9, $+, $&, $‘ and $’ in section “Special variables”. When the match has the extension modifier x attached, the following extensions can be used: With modifier x, whitespace can be used in the patters for readability purposes.

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14. Search and replace functions [ EXPR =˜ ] [ m ] /PATTERN/ [ g ] [ i ] [ m ] [ o ] [ s ] [ x ] Searches EXPR (default: $_) for a pattern. If you prepend an m you can use almost any pair of delimters instead of the slashes. If used in array context, an array is returned consisting of the sub-expressions matched by the parentheses in pattern, i.e. ($1,$2,$3,


). Optional modifiers: g matches as many times as possible; i searches in a case-insensitive manner; o interpolates variables only once. m treats the string as multiple lines; s treats the string as a single line; x use extended regular expressions. If PATTERN is empty, the most recent pattern from a previous match or replacement is used. With g the match can be used as an iterator in scalar context. ?PATTERN? This is just like the /PATTERN/ search, except that it matches only once between calls to the reset operator. [ $VAR =˜ ] s/PATTERN/REPLACEMENT/ [ e ] [ g ] [ i ] [ m ] [ o ] [ s ] [ x ] Searches a string for a pattern, and if found, replaces that pattern with the replacement text. It returns the number of substitutions made, if any, otherwise it returns false. Optional modifiers: g replaces all occurrences of the pattern; e evaluates the replacement string as an Perl expression; for the other modifiers, see /PATTERN/ matching. Almost any delimiter may replace the slashes; if single quotes are used, no interpolation is done on the strings between the delimeters, otherwise they are interpolated as if inside quoble quotes. If bracketing delimeters are used, PATTERN and REPLACEMENT may have their own delimiters, e.g. s(foo)[bar]. If PATTERN is empty, the most recent pattern from a previous match or replacement is used. [ $VAR =˜ ] tr/SEARCHLIST/REPLACEMENTLIST/ [ c ] [ d ] [ s ] Translates all occurrences of the characters found in the search list with the corresponding character in the replacement list. It returns the number of characters replaced. y may be used instead of tr. Optional modifiers: c complements the SEARCHLIST; d deletes all characters found in SEARCHLIST that do not have a corresponding character in REPLACEMENTLIST; s squeezes all sequences of characters that are translated into the same target character into one occurrence of this character. pos SCALAR

Returns the position where the last m//g search left off for SCALAR. May be used as an lvalue. study [ $VAR ] Studies the scalar variable $VAR in anticipation of doing many pattern matches on its contents before the variable is next modified.

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15. File test operators These unary operators takes one argument, either a filename or a filehandle, and test the associated file to see if something is true about it. If the argument is omitted, they test $_ (except for -t, which tests STDIN). If the special argument _ (underscore) is passed, they use the info of the preceding test or stat call. -r -w -x File is readable/writable/executable by effective uid/gid. -R -W -X File is readable/writable/executable by real uid/gid. -o -O File is owned by effective/real uid. -e -z File exists / has zero size. -s File exists and has non-zero size. Returns the size. -f -d File is a plain file, a directory. -l -S -p File is a symbolic link, a socket, a named pipe (FIFO). -b -c File is a block/character special file. -u -g -k File has setuid/setgid/sticky bit set. -t Tests if filehandle (STDIN by default) is opened to a tty. -T -B File is a text/non-text (binary) file. -T and -B return true on a null file, or a file at EOF when testing a filehandle. -M -A -C File modification / access / inode change time. Measured in days. Value returned reflects the file age at the time the script started. See also $ˆT in section “Special variables”.

16. File operations Functions operating on a list of files return the number of files successfully operated upon. chmod LIST

Changes the permissions of a list of files. The first element of the list must be the numerical mode. chown LIST

Changes the owner and group of a list of files. The first two elements of the list must be the numerical uid and gid. truncate FILE, SIZE truncates FILE to SIZE. FILE may be a filename or a filehandle. link OLDFILE, NEWFILE

Creates a new filename linked to the old filename. lstat FILE

Like stat, but does not traverse a final symbolic link. mkdir DIR, MODE

Creates a directory with given permissions. Sets $! on failure. readlink EXPR

Returns the value of a symbolic link. rename OLDNAME, NEWNAME

Changes the name of a file. rmdir FILENAME

Deletes the directory if it is empty. Sets $! on failure.

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Perl Reference Guide stat FILE

Returns a 13-element array (0:$dev, 1:$ino, 2:$mode, 3:$nlink, 4:$uid, 5:$gid, 6:$rdev, 7:$size, 8:$atime, 9:$mtime, 10:$ctime, 11:$blksize, 12:$blocks). FILE can be a filehandle, an expression evaluating to a filename, or _ to refer to the last file test operation or stat call. Returns a null list if the stat fails. symlink OLDFILE, NEWFILE

Creates a new filename symbolically linked to the old filename. unlink LIST

Deletes a list of files. utime LIST

Changes the access and modification times. The first two elements of the list must be the numerical access and modification times.

17. Input / Output In input/output operations, FILEHANDLE may be a filehandle as opened by the open operator, a pre-defined filehandle (e.g. STDOUT) or a scalar variable which evaluates to the name of a filehandle to be used. In scalar context, reads one one line from the file opened on FILEHANDLE. In array context: reads the whole file. < > Reads from the input stream formed by the files specified in @ARGV, or standard input if no arguments were supplied. binmode FILEHANDLE

Arranges for the file opened on FILEHANDLE to be read or written in “binary” mode as opposed to “text” mode (null-operation on UNIX). close FILEHANDLE

Closes the file or pipe associated with the file handle. dbmclose %HASH Deprecated, use untie instead. dbmopen %HASH, DBMNAME, MODE Deprecated, use tie instead. eof FILEHANDLE

Returns 1 if the next read will return end of file, or if the file is not open. Returns the eof status for the last file read. eof( ) Indicates eof on the pseudo file formed of the files listed on the command line. fcntl FILEHANDLE, FUNCTION, $VAR Implements the fcntl(2) function. This function has non-standard return values. See the manual for details.

eof

fileno FILEHANDLE

Returns the file descriptor for a given (open) file. flock FILEHANDLE, OPERATION Calls flock(2) on the file. OPERATION adds from 1 (shared), 2 (exclusive), 4

(non-blocking) or 8 (unlock). getc [ FILEHANDLE ] Yields the next character from the file, or "" on end of file. If FILEHANDLE is omitted, reads from STDIN.

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Perl Reference Guide ioctl FILEHANDLE, FUNCTION, $VAR

performs ioctl(2) on the file. This function has non-standard return values. See the manual for details. open FILEHANDLE [ , FILENAME ] Opens a file and associates it with FILEHANDLE. If FILENAME is omitted, the scalar variable of the same name as the FILEHANDLE must contain the filename. The following filename conventions apply when opening a file. "FILE" open FILE for input. Also "FILE" open FILE for output, creating it if necessary. ">>FILE" open FILE in append mode. "+>FILE" open FILE with read/write access. "|CMD" opens a pipe to command CMD. If CMD is “-”, forks. "CMD|" opens a pipe from command CMD. If CMD is “-”, forks. FILE may be &FILEHND in which case the new file handle is connected to the (previously opened) filehandle FILEHND. If it is &=N, FILE will be connected to the given file descriptor. open returns undef upon failure, true otherwise. pipe READHANDLE, WRITEHANDLE

Returns a pair of connected pipes. print [ FILEHANDLE ] [ LIST ] Prints the elements if LIST, converting them to strings if needed. If FILEHANDLE is omitted, prints by default to standard output (or to the last selected output channel, see select). printf [ FILEHANDLE ] LIST ] Equivalent to print FILEHANDLE sprintf LIST. read FILEHANDLE, $VAR, LENGTH [ , OFFSET ] Read LENGTH binary bytes from the file into the variable at OFFSET. Returns number of bytes actually read. seek FILEHANDLE, POSITION, WHENCE

Arbitrarily positions the file. Returns 1 upon success, 0 otherwise. select [ FILEHANDLE ] Returns the currently selected filehandle. Sets the current default filehandle for output operations if FILEHANDLE is supplied. select RBITS, WBITS, NBITS, TIMEOUT

Performs a select(2) system call with the same parameters. sprintf FORMAT, LIST

Returns a string formatted by (almost all of) the usual printf(3) conventions. sysread FILEHANDLE, $VAR, LENGTH [ , OFFSET ] Reads LENGTH bytes into $VAR at OFFSET. syswrite FILEHANDLE, SCALAR, LENGTH [ , OFFSET ] Writes LENGTH bytes from SCALAR at OFFSET. tell [ FILEHANDLE ] Returns the current file position for the file. If FILEHANDLE is omitted, assumes the file last read.

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18. Formats formline PICTURE, LIST Formats LIST according to PICTURE and accumulates the result into $ˆA. write [ FILEHANDLE ]

Writes a formatted record to the specified file, using the format associated with that file. Formats are defined as follows: format [ NAME ] = FORMLIST

. FORMLIST pictures the lines, and contains the arguments which will give values to the fields in the lines. NAME defaults to STDOUT if omitted.

Picture fields are: @>


right adjusted field; @|||


centered field; @#.##


numeric format with implied decimal point; @* a multi-line field. Use ˆ instead of @ for multi-line block filling. Use ˜ at the beginning of a line to suppress unwanted empty lines. Use ˜˜ at the beginning of a line to have this format line repeated until all fields are exhausted. Set $- to zero to force a page break. See also $ˆ, $˜, $ˆA, $ˆF, $- and $= in section “Special variables”.

19. Directory reading routines closedir DIRHANDLE

Closes a directory opened by opendir. opendir DIRHANDLE, DIRNAME

Opens a directory on the handle specified. readdir DIRHANDLE

Returns the next entry (or an array of entries) in the directory. rewinddir DIRHANDLE

Positions the directory to the beginning. seekdir DIRHANDLE, POS

Sets position for readdir on the directory. telldir DIRHANDLE

Returns the postion in the directory.

20. System interaction alarm EXPR

Schedules a SIGALRM to be delivered after EXPR seconds. chdir [ EXPR ] Changes the working directory. Uses $ENV{"HOME"} or $ENV{"LOGNAME"} if EXPR is omitted.

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Perl Reference Guide chroot FILENAME

Changes the root directory for the process and its children. die [ LIST ] Prints the value of LIST to STDERR and exits with the current value of $! (errno). If $! is 0, exits with the value of ($? >> 8). If ($? >> 8) is 0, exits with 255. LIST defaults to "Died". exec LIST

Executes the system command in LIST; does not return. exit [ EXPR ] Exits immediately with the value of EXPR, which defaults to 0 (zero). Calls END routines and object destructors before exiting. fork Does a fork(2) system call. Returns the child pid to the parent process and zero to the child process. getlogin

Returns the current login name as known by the system. getpgrp [ PID ] Returns the process group for process PID (0, or omitted, means the current process). getppid

Returns the process id of the parent process. getpriority WHICH, WHO

Returns the current priority for a process, process group, or user. glob PAT

Returns a list of filenames that match the shell pattern PAT. kill LIST

Sends a signal to a list of processes. The first element of the list must be the signal to send (numeric, or its name as a string). setpgrp PID, PGRP

Sets the process group for the PID (0 = current process). setpriority WHICH, WHO, PRIO

Sets the current priority for a process, process group, or a user. sleep [ EXPR ] Causes the script to sleep for EXPR seconds, or forever if no EXPR. Returns the number of seconds actually slept. syscall LIST

Calls the system call specified in the first element of the list, passing the rest of the list as arguments to the call. system LIST

Does exactly the same thing as exec LIST except that a fork is done first, and the parent process waits for the child process to complete. times

Returns a 4-element array (0:$user, 1:$system, 2:$cuser, 3:$csystem) giving the user and system times, in seconds, for this process and the children of this process. umask [ EXPR ] Sets the umask for the process and returns the old one. If EXPR is omitted, returns current umask value. wait Waits for a child process to terminate and returns the pid of the deceased process (-1 if none). The status is returned in $?.

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Perl Reference Guide waitpid PID, FLAGS

Performs the same function as the corresponding system call. warn [ LIST ] Prints the message on STDERR like die, but doesn’t exit. LIST defaults to "Warning: something’s wrong".

21. Networking accept NEWSOCKET, GENERICSOCKET

Accepts a new socket. bind SOCKET, NAME Binds the NAME to the SOCKET. connect SOCKET, NAME Connects the NAME to the SOCKET. getpeername SOCKET

Returns the socket address of the other end of the SOCKET. getsockname SOCKET

Returns the name of the socket. getsockopt SOCKET, LEVEL, OPTNAME

Returns the socket options. listen SOCKET, QUEUESIZE

Starts listening on the specified SOCKET. recv SOCKET, SCALAR, LENGTH, FLAGS Receives a message on SOCKET. send SOCKET, MSG, FLAGS [ , TO ] Sends a message on the SOCKET. setsockopt SOCKET, LEVEL, OPTNAME, OPTVAL

Sets the requested socket option. shutdown SOCKET, HOW Shuts down a SOCKET. socket SOCKET, DOMAIN, TYPE, PROTOCOL Creates a SOCKET in DOMAIN with TYPE and PROTOCOL. socketpair SOCKET1, SOCKET2, DOMAIN, TYPE, PROTOCOL

As socket, but creates a pair of bi-directional sockets.

22. SystemV IPC msgctl ID, CMD, ARGS

Calls msgctl(2). If CMD is &IPC_STAT then ARG must be a variable. msgget KEY, FLAGS

Creates a message queue for KEY. Returns the message queue id. msgsnd ID, MSG, FLAGS Sends MSG to queue ID. msgrcv ID, $VAR, SIZE, TYPE, FLAGS Receives a message from queue ID into VAR. semctl ID, SEMNUM, CMD, ARG

Calls semctl(2). If CMD is &IPC_STAT of &GETALL then ARG must be a variable.

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Perl Reference Guide semget KEY, NSEMS, SIZE, FLAGS

Creates a set of semaphores for KEY. Returns the message semaphore id. semop KEY, ... Performs semaphore operations. shmctl ID, CMD, ARG

Calls shmctl(2). If CMD is &IPC_STAT then ARG must be a variable. shmget KEY, SIZE, FLAGS

Creates shared memory. Returns the shared memory segment id. shmread ID, $VAR, POS, SIZE Reads at most SIZE bytes of the contents of shared memory segment ID starting at offset POS into VAR. shmwrite ID, STRING, POS, SIZE Writes at most SIZE bytes of STRING into the contents of shared memory segment ID at offset POS.

23. Miscellaneous defined EXPR

Tests whether the lvalue EXPR has an actual value. do FILENAME

Executes FILENAME as a perl script. See also require in section “Subroutines, packages and modules”. dump [ LABEL ] Immediate core dump. When reincarnated, starts at LABEL. eval{EXPR;


} Executes the code between { and }. Traps runtime errors as described with eval(EXPR), section “String functions” . local LIST

Creates a scope for the listed variables local to the enclosing block, subroutine or eval. my LIST

Creates a scope for the listed variables lexically local to the enclosing block, subroutine or eval. ref EXPR

Returns a true value if EXPR is a reference. Returns the package name if EXPR has been blessed into a package. reset [ EXPR ] Resets ?? searches so that they work again. EXPR is a list of single letters. All variables and arrays beginning with one of those letters are reset to their pristine state. Only affects the current package. scalar EXPR

Forces evaluation of EXPR in scalar context. undef [ LVALUE ] Undefines the LVALUE. Always returns the undefined value. wantarray

Returns true if the current context expects an array value.

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24. Info from system files See the manual about return values in scalar context.

passwd Returns ($name, $passwd, $uid, $gid, $quota, $comment, $gcos, $dir, $shell). endpwent Ends lookup processing. getpwent Gets next info. getpwnam NAME Gets info by name. getpwuid UID Gets info by uid. setpwent Resets lookup processing.

group Returns ($name, $passwd, $gid, $members). endgrent Ends lookup processing. getgrgid GID Gets info by group id. getgrnam NAME Gets info by name. getgrent Gets next info. setgrent Resets lookup processing.

hosts Returns ($name, $aliases, $addrtype, $length, @addrs). endhostent Ends lookup processing. gethostbyaddr ADDR, ADDRTYPE Gets info by address. gethostbyname NAME Gets info by name. gethostent Gets next info. sethostent STAYOPEN Resets lookup processing.

networks Returns ($name, $aliases, $addrtype, $net). endnetent Ends lookup processing. getnetbyaddr ADDR, TYPE Gets info by address and type. getnetbyname NAME Gets info by name. getnetent Gets next info. setnetent STAYOPEN Resets lookup processing.

services Returns ($name, $aliases, $port, $proto). endservent Ends lookup processing. getservbyname NAME, PROTO Gets info by name. getservbyport PORT, PROTO Gets info by port. getservent Gets next info. setservent STAYOPEN Resets lookup processing.

protocols Returns ($name, $aliases, $proto). endprotoent getprotobyname NAME getprotobynumber NUMBER getprotoent setprotoent STAYOPEN

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Ends lookup processing. Gets info by name. Gets info by number. Gets next info. Resets lookup processing.

Perl Reference Guide

25. Special variables The following variables are global and should be localized in subroutines: $_ The default input and pattern-searching space. $. The current input line number of the last filehandle that was read. $/ The input record separator, newline by default. May be multi-character. $, The output field separator for the print operator. $" The separator which joins elements of arrays interpolated in strings. $\ The output record separator for the print operator. $# The output format for printed numbers. Deprecated. $* Set to 1 to do multiline matching within strings. Deprecated, see the m and s modifiers in section “Search and replace functions”. $? The status returned by the last ‘COMMAND‘, pipe close or system operator. $] The perl version number. $[ The index of the first element in an array, and of the first character in a substring. Default is 0. Deprecated. $; The subscript separator for multi-dimensional array emulation. Default is "\034". $! If used in a numeric context, yields the current value of errno. If used in a string context, yields the corresponding error string. $@ The perl error message from the last eval or do EXPR command. $: The set of characters after which a string may be broken to fill continuation fields (starting with “ˆ”) in a format. $0 The name of the file containing the perl script being executed. May be assigned to. $$ The process number of the perl running this script. Altered (in the child process) by fork. $< The real uid of this process. $> The effective uid of this process. $( The real gid of this process. $) The effective gid of this process. $ˆA The accumulator for formline and write operations. $ˆD The debug flags as passed to perl using -D . $ˆF The highest system file descriptor, ordinarily 2. $ˆI In-place edit extension as passed to perl using -i . $ˆL Formfeed character used in formats. $ˆP Internal debugging flag. $ˆT The time (as delivered by time) when the program started. This value is used by the file test operators -M, -A and -C. $ˆW The value if the -w option as passed to perl. $ˆX The name by which this perl was invoked. The following variables are context dependent and need not be localized: $% The current page number of the currently selected output channel. $= The page length of the current output channel. Default is 60 lines. $- The number of lines left on the page. $˜ The name of the current report format.

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Perl Reference Guide The name of the current top-of-page format. If set to nonzero, forces a flush after every write or print on the currently selected output channel. Default is 0. $ARGV The name of the current file when reading from < > . The following variables are always local to the current block: $& The string matched by the last successful pattern match. $‘ The string preceding what was matched by the last successful match. $’ The string following what was matched by the last successful match. $+ The last bracket matched by the last search pattern. $1


$9


Contain the subpatterns from the corresponding sets of parentheses in the last pattern successfully matched. $10


and up are only available if the match contained that many subpatterns.

$ˆ $|

26. Special arrays @ARGV Contains the command line arguments for the script (not including the command name). @EXPORT Names the methods a package exports by default. @EXPORT_OK Names the methods a package can export upon explicit request. @INC Contains the list of places to look for perl scripts to be evaluated by the do FILENAME and require commands. @ISA List of “base classes” of a package. @_ Parameter array for subroutines. Also used by split if not in array context. %ENV Contains the current environment. %INC List of files that have been required or done. %OVERLOAD Can be used to overload operators in a package. %SIG Used to set signal handlers for various signals.

27. Environment variables Perl uses the following environment variables. HOME Used if chdir has no argument. LOGDIR Used if chdir has no argument and HOME is not set. PATH Used in executing subprocesses, and in finding the perl script if -S is used. PERL5LIB A colon-separated list of directories to look for perl library files before looking in the standard library and the current directory. PERL5DB The command to get the debugger code. Defaults to BEGIN { require ’perl5db.pl’ }. PERLLIB Used instead of PERL5LIB if the latter is not defined.

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28. The perl debugger The perl symbolic debugger is invoked with “perl -d”. h Prints out a help message. T Stack trace. s Single steps. n Single steps around subroutine call. RET Repeats last s or n. r Returns from the current subroutine. c [ LINE ] Continues (until LINE, or another breakpoint or exit). p EXPR Prints EXPR. l [ RANGE ] Lists a range of lines. RANGE may be a number, start-end, start+amount, or a subroutine name. If omitted, lists next window. Lists previous window. w Lists window around current line. f FILE Switches to FILE and start listing it. l SUB Lists the named SUBroutine. S List the names of all subroutines. /PATTERN/ Forward search for PATTERN. ?PATTERN? Backward search for PATTERN. b [ LINE [ CONDITION ]] Sets breakpoint at LINE, default: current line. b SUBNAME [ CONDITION ] Sets breakpoint at the subroutine. d [ LINE ] Deletes breakpoint at the given line. D Deletes all breakpoints. L Lists lines that have breakpoints or actions. a LINE COMMAND Sets an action for line. A Deletes all line actions. < COMMAND Sets an action to be executed before every debugger prompt. > COMMAND Sets an action to be executed before every s, c or n command. V [ PACKAGE [ VARS ] ] Lists all variables in a package. Default package is main. X [ VARS ] Like V, but assumes current package. ! [ [-]NUMBER ] Redo a debugging command. Default is previous command. H [ -NUMBER ] Displays the last -NUMBER commands of more than one letter. t Toggles trace mode. = [ ALIAS VALUE ] Sets alias, or lists current aliases. q Quits. You may also use your EOF character. COMMAND Executes COMMAND as a perl statement.

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Notes

Perl Reference Guide Revision 5.000.0

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c 1989,1995 Johan Vromans